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package org.apache.juneau.http;

/**
 * Represents a parsed <l>Age</l> HTTP response header.
 * 
 * <p>
 * The age the object has been in a proxy cache in seconds.
 * 
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 * 	Age: 12
 * </p>
 * 
 * <h5 class='topic'>RFC2616 Specification</h5>
 * 
 * The Age response-header field conveys the sender's estimate of the amount of time since the response (or its
 * revalidation) was generated at the origin server.
 * A cached response is "fresh" if its age does not exceed its freshness lifetime.
 * Age values are calculated as specified in section 13.2.3.
 * 
 * <p class='bcode'>
 * 	Age = "Age" ":" age-value
 * 	age-value = delta-seconds
 * </p>
 * 
 * <p>
 * Age values are non-negative decimal integers, representing time in seconds.
 * 
 * <p>
 * If a cache receives a value larger than the largest positive integer it can represent, or if any of its age
 * calculations overflows, it MUST transmit an Age header with a value of 2147483648 (2^31).
 * 
 * <p>
 * An HTTP/1.1 server that includes a cache MUST include an Age header field in every response generated from its own
 * cache.
 * 
 * <p>
 * Caches SHOULD use an arithmetic type of at least 31 bits of range.
 * 
 * <h5 class='section'>See Also:</h5>
 * <ul class='doctree'>
 * 	<li class='extlink'><a class='doclink' href='https://www.w3.org/Protocols/rfc2616/rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a>
 * </ul>
 */
public final class Age extends HeaderInteger {

	/**
	 * Returns a parsed <code>Age</code> header.
	 * 
	 * @param value The <code>Age</code> header string.
	 * @return The parsed <code>Age</code> header, or <jk>null</jk> if the string was null.
	 */
	public static Age forString(String value) {
		if (value == null)
			return null;
		return new Age(value);
	}

	private Age(String value) {
		super(value);
	}
}
